FIG. 1 illustrates the configuration and use mode of an existing storage system 200 having a remote copy function. Note that the storage system 200 that will be described below is a system which can increase total storage capacity by increasing the number of storage devices 220 (usually, hard disk drive) to be installed in a casing. Also, the storage system 200 is also a system wherein a particular storage device 220 is controlled by each of multiple control modules 210 installed in the casing.
As illustrated in FIG. 1, the storage system 200 is used in a state connected to a host 300 and another storage system 200 (hereafter, referred to as “copy destination system 200”) installed at a remote location. Multiple sets of control data storage area 201 and updated data storage area 202 are provided within each control module 210 of the storage system 200 (hereafter, referred to as “copy source system 200”) connected to the host 300. Also, multiple sets of control data storage area 201 and updated data storage area 202 are also provided within each control module 210 of the copy destination system 200. Note that the control modules 210 are units made up of a combination of a CPU (Central Processing Unit), RAM (Random Access Memory), and so forth, and the control data storage areas and updated data storage areas are both storage areas on the RAM.
Control data storage area 201 and updated data storage area 202 of one set within each control module 210 are mutually correlated as storage areas belonging to one buffer set 203. Each control module 210 within the copy source system 200 operates as follows.
In the event of having received a write request for certain updated data from the host 300, each control module 210 performs storing of write destination information, and storing of control data in control data storage area 201 belonging to a certain buffer set 203 (hereafter, referred to as “buffer set 0”), and then responds to this write request. The write destination information mentioned here is information indicating the writing position of updated data. Also, the control data mentioned here is information indicating the writing position in the copy destination system 200 of updated data.
Also, each control module 210 within the copy source system 200 performs processing for reading out updated data from the storage device 220 based on the write destination information to store the updated data in updated data storage area 202 belonging to the buffer set 0.
Further, in the event that new control data is not storable in the control data storage area 201 within any of the control modules 210, or the like, each control module 210 within the copy source system 200 switches the buffer set in a synchronous manner. Specifically, each control module 210 stores control data and updated data in a control data storage area 201 and an updated data storage area 202 belonging to a buffer set 1 respectively, for example.
Each control module 210 within the copy source system 200 sequentially transmits, after storing of updated data in the updated data storage area 202 belonging to the buffer set 0 is completed, information on each storage area belonging to the buffer set 0 to the copy destination system 200.
Each control module 210 within the copy destination system 200 temporarily internally stores the transmitted information as information regarding the buffer set 0. Each control module 210 within the copy destination system 200 performs, in the event that all of information regarding the buffer set 0 have been collected within the own system 200, writing of contents that information held by itself (a plurality of updated data and control data relating to each updated data) indicates as to the storage device 220.
Japanese Laid-open Patent Publication Nos. 2006-260292, 2010-039574, 2011-086160, 2011-086006, 2003-167683, 7-244597 and 2003-122509, and International Publication Pamphlet No. WO 2008-152691 are examples of related art.
Briefly, in the event that the above-mentioned storage system 200 (hereafter, referred to as “existing SS 200”) is used in a form illustrated in FIG. 1, an environment can be realized wherein data within the copy destination system 200 is periodically backed up within the copy source system 200. Accordingly, when the existing SS 200 is used in a form such as illustrated in FIG. 1, in the event that the copy source system 200 is not usable due to a disaster or the like, operation can be resumed using the copy destination system 200.
However, in the event that shortage in storage capacity is not handleable by addition to the storage device 220, the existing SS 200 itself has to be replaced with a system having larger capacity.
Specifically, in the event of connecting another existing SS 200 to the host 300, the storage capacity on the host 300 side (storage capacity that the host 300 can use for storage of data) can be extended. Also, in the event of adding another existing SS 200 (hereafter, referred to as “second copy destination system 200”) at a remote location, data within the existing SS 200 (hereafter, referred to as “second copy source system 200”) added to the host 300 side can be backed up within the second copy destination system 200.
However, remote copy between the added two systems is performed completely unrelated to remote copy between the original copy source/copy destination systems 200 (hereafter, referred to as “first copy source/first copy destination systems 200”). Accordingly, with a system where the four existing SS 200 are combined, there may be a case where data within the first copy destination system 200 becomes backed up data within the first copy source system 200 at certain point-in-time T1, and data within the second copy destination system 200 becomes backed up data within the second copy source system 200 at another point-in-time T2 (e.g., point-in-time different from T1 by 30 minutes).
When backed up data within the first and second copy destination systems 200 are as mentioned above, there may be a case where operation is not resumable using the first and second copy destination systems 200 (e.g., databases are stored in the first and second copy source systems 200 in a distributed manner). Therefore, in the case of employing an existing SS 200, when storage capacity that is handleable with addition to the storage device 220 is not large enough, the system itself has to be replaced with a system having larger capacity.